The present invention relates to devices and methods for estimating spatial orientations of mobile terminal devices, as they are used, in particular, for localizing or navigating the mobile terminal devices in a wireless communication network.
For a localization of mobile terminal devices, different localization technologies are available. The probably most common system for localization or navigation in the outdoor area is the satellite-supported global positioning system (GPS). For the localization or navigation within buildings or in an indoor area, different approaches are known, like, for example, infrared systems, HFID systems or also field-strength evaluations of IEEE 802.11 WLAN networks (wireless local area networks). The GPS system is currently only reliably available for the outdoor area. New expansions, like, for example, highly sensitive receivers or the so-called A-GPS (assisted GPS) represent approaches to make the technology also usable within buildings. A-GPS here combines the use of the satellite-based GPS system with a reception of so-called assistance information from cellular mobile radio networks. Currently, these technologies do not have the desired average accuracies. Infrared systems and HFID systems are generally not available everywhere and are bound to specific conditions.
Based on the increasing spread of wireless radio networks, for example based on the WLAN standard, these wireless networks offer themselves as a basis for new localization methods.
Conventional localization methods used hitherto are based, for example, on triangulation, neighborhood relationships, lateration by means of time measurement or lateration by means of field strength evaluation. These are localization methods, wherein either the position of stationary radio transmitters or base stations has to be known or wherein training has to be done beforehand at reference positions in an environment to be covered by the localization method.
With WLAN-based localization systems, often a so-called received signal strength (RSS) fingerprinting is used as a basic method. This method is based on the assumption that signal strengths of radio signals of several radio stations received or receivable at a certain location uniquely characterize the current location or the current position. If a reference database exists, containing, for a number of reference locations or reference positions, transmitter identifications of radio stations received or receivable there at reference times and the signal strengths of the corresponding radio signals, then from a set of current measurement values (transmitter identifications and associated signal strength values) the current position may be concluded by executing a matching between the currently measured measurement values and the reference values of the database. This matching evaluates, for each reference point, how similar the previously recorded measurement values or reference values are compared to the current measurement values of the current position. The one or several most similar reference points then form a basis for an estimate for the current location of the mobile terminal device.
For a reference database, by a reference measurement the signal strength of a radio transmitter receivable at a reference measurement time at a reference position is determined by experiment. From this, a database results containing, for each reference position at which a reference measurement was executed, a list of radio transmitters (access points) with the respectively associated receive field strength and quality. This list may also be referred to as a reference package. With a WLAN implementation, such a reference database may, for example, contain the following parameters:
RIDMACRSSIPGSXYZMAPNRCREATED100.0D.54.9E.17.8146530100579515627150012.03.07 12:42100.0D.54.9E.1A.BA6726090579515627150012.03.07 12:42100.0D.54.9E.1D.647200288579515627150012.03.07 12:42100.0E.6A.D3.B9.8B59531100579515627150012.03.07 12:42100.0F.A3.10.07.6C4646496579515627150012.03.07 12:42100.0F.A3.10.07.FB7448894579515627150012.03.07 12:42100.0F.A3.10.09.SF7237597579515627150012.03.07 12:42200.0D.54.9E.17.81541381001439915451150012.03.07 12:43200.0D.54.9E.18.1D76560111439915451150012.03.07 12:43200.0D.54.9E.1A.BA62318941439915451150012.03.07 12:43200.0D.54.9E.1D.6471348961439915451150012.03.07 12:43200.0E.6A.D3.B9.8B453931001439915451150012.03.07 12:43200.0F.A3.10.07.6C66853961439915451150012.03.07 12:43200.0F.A3.10.07.FB722511001439915451150012.03.07 12:43200.0F.A3.10.09.5F70990901439915451150012.03.07 12:43300.0D.54.9E.17.81582911002458315627150012.03.07 12:43300.0D.54.9E.18.1D78610682458315627150012.03.07 12:43300.0D.54.9E.1A.BA62153982458315627150012.03.07 12:43300.0D.54.9E.1D.6464187902458315627150012.03.07 12:43300.0E.6A.D3.B9.8B328511002458315627150012.03.07 12:43300.0F.A3.10.07.6C69006962458315627150012.03.07 12:43300.0F.A3.10.07.FB71749922458315627150012.03.07 12:43300.0F.A3.10.09.5F71482832458315627150012.03.07 12:43300.0F.A3.10.09.8071000402458315627150012.03.07 12:43
Here, the table contains the following information:                the reference position identification (RID)        the MAC addresses (MAC=media access control) of the received stations        the receive field strengths of the radio transmitters (RSSI (received signal strength indicator); 46560 means −46,560 dBm)        the reference position in Cartesian, metrical coordinates (x, y, z; 24583 means 245.83 m) and        the time of measurement value recording.        
The column PGS (“percentage seen”) indicates how often this station was seen in percent in measurement value recording (i.e. PGS=90 means that on average the station was measured in 9 out of 10 measurements).
In the above-illustrated table, any information associated with a reference position identification (RID) corresponds to a reference measurement package. I.e. the above-indicated exemplary table includes three reference measurement packages corresponding to three different geographical reference positions.
For the localization currently received radio transmitters with their respectively associated receive field strength (measurement package) are compared to reference packages from the reference database in a matching phase. A conventional distance formula often used in the matching phase is
                    acc        =                              ∑                          n              =              1                        Neq                    ⁢                      Δ            ⁢                                                  ⁢                          RSSI              n                                                          (        1        )            and it is here assumed that all radio transmitters may be received everywhere. Here, acc refers to the accordance measure or the distance between the current measurement package and the reference package and Neq to a number of radio transmitters, wherein previously recorded transmitter identifications at the reference position are identical to transmitter identifications provided at the current position. Differences of RSSI values of radio transmitters, wherein previously recorded transmitter identifications at the reference position are identical to the transmitter identifications provided at the current position are referred to as ΔRSSIn (n=1, . . . Neq). It is not in every case the case, however, that all radio transmitters may be received everywhere. If a reference package contains radio transmitters A, B and C, and a current measurement package contains the radio transmitters D, E, an (optimum) value 0 results as the distance. Apparently the reference package fits perfectly, although not one single radio transmitter matches between the reference and the current measurement package.
Thus, for practice, the calculation of the accordance or the distance may be varied such that in a current measurement package as compared to a reference measurement package too many or too few received radio transmitters increase the distance by a value which results, for example, from a malus function.
                    acc        =                                                                                                  EQW                    ·                                                                  ∑                                                  n                          =                          1                                                Neq                                            ⁢                                              Δ                        ⁢                                                                                                  ⁢                                                                              RSSI                            n                                                    ⁡                                                      (                                                                                                                  )                                                                                                                                +                                                            (                                              1                        -                        EQW                                            )                                        ·                                                                                                                        (                                                                                    ∑                                                  m                          =                          1                                                                          N                          nh                                                                    ⁢                                                                        M                                                      nh                            ,                            m                                                                          ⁡                                                  (                                                                                                          )                                                                                      +                                                                  ∑                                                  r                          =                          1                                                                          N                          HTM                                                                    ⁢                                                                        M                                                      htm                            ,                            r                                                                          ⁡                                                  (                                                                                                          )                                                                                                      )                                                                                        N              eq                        +                          N              nh                        +                          N              htm                                                          (        2        )            
Here, EQW designates a weight between 0 and 1 which indicates how highly the distance of the measurement values or the distance of the signal strength values ΣΔRSSIn at the current position is to be rated compared to the too many (Nnh) or too few (Nhtm) radio transmitters received. For each radio transmitter which is missing in the reference values, but which is contained in the currently measured measurement values, a malus value Mhtm,r( ) (r−1, . . . , Nhtm) may be defined. Likewise, for each radio transmitter which is contained in the references values but is missing in the currently measured measurement values, a malus value Mnh,m( ) (m−1, . . . , Nnh) may be defined.
Reference packages with a small distance to the current measurement package, i.e. many common radio transmitters and few different receive field strengths, fit well into the current measurement package. The reference positions belonging to the well fitting reference packages are very probable and enter a position calculation phase. The position calculation phase calculates the position of the mobile terminal device from the candidate positions. The result of this phase is the position of the terminal device. One possible realization is the calculation of a weighted average value from the candidate positions of the matching phase. The inverse distance values here form the weights in the averaging. This method called k-weighted nearest neighbor provides respectable results, the average positioning error being a few meters.
If a user is holding a mobile terminal device, like, e.g., a PDA (personal digital assistant) in front of his body, radio signals of radio transmitters behind the user's body may be strongly attenuated. If the user is now, for example, close to a reference position for which a reference package exists in a reference database, the reference package is discarded as not very suitable due to the signal attenuation by the body, as the shadowed radio transmitters were not shadowed during calibration, or shadowed to a lesser extent, and thus the radio fingerprints are not a good match.
It may also happen that a mobile terminal device which was used for calibrating the reference packages comprises another antenna directional pattern or characteristic than the mobile terminal device used by a user for localizing or navigating. For this reason and in addition to the alignment of the mobile terminal device with the body, it may happen that reference packages of reference positions which actually match well are erroneously discarded and that a position estimation is thus adversely affected.
In addition, it may be of interest for some applications to obtain information about the orientation of the mobile terminal device to the body or the spatial orientation of the user and/or terminal device.